This invention is in the field of condensation particle counters or condensation nuclei counters. In an embodiment, provided herein are systems and methods that prevent the migration of condensate from components of the system designed to contain condensate (e.g. condensate reservoir, saturator, or condenser) to components which may be damaged or interfered with by the presence of a condensate (e.g. particle counters, optical components of an optical particle counter, and flow control devices such as orifices).
A large portion of the micro-contamination industry and clean manufacturing industries is reliant on the use of particle counters, such as are described in a number of U.S. Patents, including U.S. Pat. Nos. 3,851,169, 4,348,111, 4,957,363, 5,085,500, 5,121,988, 5,467,188, 5,642,193, 5,864,399, 5,920,388, 5,946,092, and 7,053,783. Particle counters are also described in U.S. Pat. Nos. 4,728,190, 5,282,151, 6,859,277, and 7,030,980, which are hereby incorporated by reference in their entirety.
A conventional condensation particle counter allows for the detection of small particles using relatively low sensitivity particle counter devices, for example optical particle counters, by increasing detectability of the particle by condensing a vapor into a liquid on the particles' surface, increasing the apparent volume of the particle. The fluid being condensed on the particle is commonly referred to as the condensate or working fluid. Typically, a sample to be analyzed enters the condensation particle counter system through a flow control device (e.g. a flow orifice) and into a saturator where the sample is mixed with a concentration of condensate primarily in the vapor form. The saturator is in fluid communication with a condensate reservoir which provides condensate to the saturator, where it is heated to ensure it is sufficiently in the vapor phase. The sample stream, now mixed with condensate vapor, then flows into a condenser which cools the sample stream, causing the condensate to condense as a liquid around particles contained in the sample stream, thereby enlarging the perceived particle by creating a layer of liquid around the particle. The sample stream is then provided to a particle detection system, such as an optical particle counter, which more easily detects the particle due to the larger signature caused by the liquid layer.
Many different fluids are suitable as working fluids, but common examples include alcohols, water and glycerol. Depending on the particle detection device, the condensate may be harmful if allowed to interact with the sensitive components of the detection system or problematic if allowed to interfere with the small volumes of the flow control devices. Thus, problems can arise when the condensation particle counter system is moved, either within a laboratory or transported to a different destination, as the condensate may migrate away from the saturator and condenser components and into the optics or flow control devices. This problem is compounded if the system is not maintained in an upright position during transportation, as the saturator and condenser are often positioned to prevent condensate migration while the system is upright.
These problems are further magnified when a viscous and/or wettable condensate (e.g. glycerol) is used in the condensation particle counter system. While viscous and/or wettable condensates provide certain advantages in operation of the condensation particle counter, the higher viscosity and wettability increases the propensity of the working fluid to be retained in the device and, thus, available to migrate to different device components even after the device has been drained to remove condensate. This leads to condensate migration problems during shipping, even if the condensate reservoir has been drained and device is shipped or transported after the vast majority of the condensate has been removed.
It can be seen from the foregoing that there remains a need in the art for systems and methods which prevent the migration of condensate in a condensation particle counter to protect sensitive components.